Mosquitoes like this female Aedes (Ochlerotatus) sp., sucking blood to get nourishment for her eggs, can transmit the viruses that cause West Nile fever and Rift Valley fever.

Two cases of eastern equine encephalitis (EEE) in horses in a short space of time has prompted a warning from health officials in Marion County, Florida.

The Florida Department of Health in Marion County has issued a mosquito-borne illnesses advisory in response to an increase in mosquito-borne disease activity in areas of Marion County.

On June 29, a second horse in less than two weeks tested positive for the EEE virus. This was the fourth horse to test positive for the virus in Marion County in 2014, the department said.

Horses also tested positive on April 22, May 31 and June 19.

The risk of transmission to humans has increased, it said, and the department was continuing surveillance and prevention efforts.

“With two eastern equine encephalitis infections confirmed in such a short span of time, it is prudent to issue a mosquito-borne illnesses advisory,” said Dan Dooley, environmental administrator for the department.

“Residents and visitors need to avoid being bitten by mosquitoes and to take basic precautions to help limit exposure to mosquitoes that can carry diseases.”